1. Field of the Invention
The present invention relates to a servo control method and apparatus of a data storage system, and more particularly, to a method and apparatus for compensating for a frequency component affecting servo control performance in a system.
This U.S. non-provisional patent application claims priority under 35 U.S.C §119 of Korean Patent Application No. 10-2006-0062979 filed on Jul. 5, 2006, the entire contents of which are hereby incorporated by reference.
2. Discussion of Related Art
In general, a hard disk drive (HDD) is a combination of a head disk assembly (HDA) comprised of mechanical components and an electrical circuit. A harmful resonance is generated by a head stack assembly (HSA), a disk, and a motor which are components of the HDD. This resonance directly affects a Position Error Signal (PES) resulting in a decrease of stability of servo control of the HDD. The decrease of stability causes a decrease in data reliability.
Korean Patent Application No. 10-0518553 suggests a technique of detecting a resonance frequency by vibrating a system each time the system is used. The detected resonance frequency is compensated for by using a notch filter. Korean Patent Application No. 10-0377844 suggests a technique of compensating for an influence of a resonance frequency using at least one programmable filter provided in each servo loop.
As illustrated in FIG. 8, the PES is affected by a disk mode representing a resonance caused by a disk and an arm bending mode representing a resonance caused by an assembly state of an actuator arm. Previous methods to solve this problem removed the resonance frequency affecting the HDD by filtering or screening based on a frequency of a PES. Filters used to remove the resonance frequency are designed in an initial development stage based on a resonance frequency component extracted from PESs of a predetermined number of HDDs and commonly applied to all HDDs. However, resonance frequencies change according to characteristics of various components forming an HSA assembly, as well as the characteristics of each assembly. As illustrated in FIG. 11, a plurality of HDDs â-ê have different resonance frequencies. The resonance frequency differences between HSA assemblies having different characteristics cannot be solved by a loop filter or a notch filter using fixed filter parameters commonly applied to all HDDs.